Nanometric surface design has been a research focus over the past decade, with a variety of concepts and methods developed. Most produce features with a size scale greater than 100 nm (e.g., standard photolithography, microcontact printing and/or with regularity interference methods). Such methods are labor or equipment intensive. Consider, for instance, the fabrication of a lithographic mask for the fabrication of a complex mold to produce stamps for microcontact printing. Scribe-type methods (AFM-writing, e-beam lithography, with nanometric resolution) are not only both labor and equipment intensive, but are also substantially limited in terms of surface chemistry. Only recently have interference methods been applied to e-beam lithography, but at the cost of production limited only to regular patterns.
Concurrently, increasing effort has been made to design and fabricate surfaces with selective properties, for use in conjunction with tissue scaffolds, sensors, smart adhesives, separation media, etc. Selectivity has been most often achieved, borrowing directly from biology, by the covalent attachment of biomolecular fragments (both polypeptide and DNA), and the passivation of remaining surface area. The resulting surfaces bind target molecules, often in micron and slightly submicron patterns that form the basis for array devices. While there is much to be gained by direct incorporation of biomolecules or biomimetic analogs, such systems tend to be technically narrow and limited to detection of specific sensor-analyte chemical or immunological interactions. Incorporation of biological molecules or fragments also can limit device lifetime and usage conditions, since biological molecules are often readily degraded.
Most patterned surfaces made by the foregoing techniques are designed to store information or provide arrays for addressable multi-element sensing. Wherein such arrays are used for sensor elements, biological molecules (DNA, proteins and antibodies) are placed in various parts of the array, thereby imparting specificity to each array element. Informational density and sensitivity can be but are not necessarily promoted by decreasing sensor size and/or adding more or different sensor elements. As a result, improved detection continues to present on-going fabrication challenges.